Fuel cell system and power control method therefor

This is a 371 national phase application of PCT/JP2009/060423 filed 8 Jun. 2009, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a fuel cell system mounted on a vehicle, and particularly relates to a fuel cell system having two DC-DC converters.

BACKGROUND ART

As a fuel cell system mounted on a vehicle, a system having a plurality of DC-DC converters has been developed. For example, Patent Publication JP-A-2007-209161 discloses a fuel cell system having a first DC-DC converter disposed between a power storage device and an inverter and a second DC-DC converter disposed between a fuel cell and the inverter.

In the system, when a target motor output is larger than a predetermined threshold value, the first DC-DC converter is turned off, the second DC-DC converter is set into a directly connected state, and the output power of the fuel cell having high output is supplied to a motor in preference to the output power of the power storage device. On the other hand, when the target motor output is lower than the predetermined threshold value, the first DC-DC converter is operated to cause assistance power to be supplied from the power storage device, and the second DC-DC converter is put in an electrically directly connected state. With such configuration, the running performance of a vehicle has been prevented from being lowered, and effective power conversion has been allowed (Patent Literature 1).

CITATION LIST

Patent Literature

<ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0005">[Patent Literature 1] Patent Publication JP-A-2007-209161</li></ul>

SUMMARY OF INVENTION

Technical Problem

However, in the invention according to Patent Literature 1 described above, since the DC-DC converter has been switched between the first and second DC-DC converters on the basis of the output power of the motor, the output voltage of the fuel cell has become higher than the input voltage of the inverter in some cases. In such a case, although it is not necessary to increase the output voltage of the fuel cell, it follows that the DC-DC converter (the second DC-DC converter in Patent Literature 1) is unnecessarily driven. That is, the operation power of the converter is unnecessarily consumed.

In view of the foregoing, in order to solve the above-described problem, in a preferred aspect of the invention of the present application, an object thereof is to provide a fuel cell system capable of reducing power consumption by inhibiting the unnecessary operation of the DC-DC converter, and a power control method therefor.

Solution to Problem

An aspect of the fuel cell system for solving the above-described problem includes an inverter which is connected to a load device, a first converter which is connected between a fuel cell and the inverter and sets an output voltage of the fuel cell, a second converter which is connected between a power storage device and the inverter and sets an input voltage of the inverter, and a control device which controls the first converter and the second converter, and the control device causes a higher voltage of a required output voltage of the fuel cell and a required input voltage of the inverter to be outputted as the input voltage of the inverter.

According to such configuration, since the higher one of the required output voltage of the fuel cell and the required input voltage of the inverter is selected, the output voltage of the fuel cell is prevented from being higher than the input voltage of the inverter. Therefore, it is possible to inhibit an unnecessary operation of the first converter.

Specifically, the control device compares the required output voltage of the fuel cell and the required input voltage of the inverter, and causes the operation of the first converter to be suspended when judgment is made that the required output voltage of the fuel cell is not less than the required input voltage of the inverter.

That is, another aspect of the fuel cell according to the present invention is a fuel cell system having an inverter which is connected to a load device, a first converter which is connected between a fuel cell and the inverter and sets an output voltage of the fuel cell, and a second converter which is connected between a power storage device and the inverter and sets an input voltage of the inverter, the fuel cell system including: fuel cell required output voltage calculation means for calculating a required output voltage of the fuel cell; inverter required input voltage calculation means for calculating a required input voltage of the inverter; comparison means for comparing the required output voltage of the fuel cell and the required input voltage of the inverter; and converter operation control means for causing an operation of the first converter to be suspended when judgment is made that the required output voltage of the fuel cell is not less than the required input voltage of the inverter.

In addition, an aspect of the power control method for the fuel cell according to the present invention is a power control method for a fuel cell system having an inverter which is connected to a load device, a first converter which is connected between a fuel cell and the inverter and sets an output voltage of the fuel cell, and a second converter which is connected between a power storage device and the inverter and sets an input voltage of the inverter which includes the steps of calculating a required output voltage of the fuel cell, calculating a required input voltage of the inverter, comparing the required output voltage of the fuel cell and the required input voltage of the inverter, and causing an operation of the first converter to be suspended when it is judged that the required output voltage of the fuel cell is not less than the required input voltage of the inverter.

According to such configuration, when it is judged that the required output voltage of the fuel cell is not less than the required input voltage of the inverter, the operation of the first converter is inhibited, and hence it is possible to prevent an unnecessary power conversion operation.

In the present invention, if desired, it is possible to selectively add the following elements.

(1) The first converter preferably maintains the fuel cell and the inverter in an electrically connected state while the operation of the first converter is suspended. With this configuration, the required input voltage of the inverter serves as the output voltage of the fuel cell while the operation of the first converter is suspended, and hence it is possible to establish a low-efficiency operation state based on the power supply from the power storage device.

(2) When judgment is made that the required output voltage of the fuel cell is not less than a voltage obtained by adding a first margin voltage to the required input voltage of the inverter, it is preferable to suspend the operation of the first converter. According to such configuration, only after the required output voltage of the fuel cell becomes not less than the voltage obtained by adding the first margin voltage corresponding to the margin at the time of the suspension to the required input voltage of the inverter, the suspension condition of the first inverter is assumed to be satisfied. As a result, after the required output voltage of the fuel cell becomes not less than the required input voltage of the inverter, slight waiting time is spent on waiting, and hence it is possible to suspend the first converter after the input voltage of the inverter reliably becomes higher than the output voltage of the fuel cell. Therefore, it is possible to reliably suppress unnecessary power consumption.

(3) When judgment is made that the required output voltage of the fuel cell is lower than a voltage obtained by adding a second margin voltage to the required input voltage of the inverter, it is preferable to start the operation of the first converter after second waiting time elapses. According to such configuration, only after it is judged that the required output voltage of the fuel cell is lower than the voltage obtained by adding the second margin voltage corresponding to the margin at the time of the start of the operation to the required input voltage of the inverter, the operation start condition of the first inverter is assumed to be satisfied. As a result, the operation of the first inverter is started before the required output voltage of the fuel cell becomes lower than the required input voltage of the inverter, and hence it is possible to start the power conversion of the fuel cell without the delay of response. Therefore, it is possible to prevent the shortage of power supplied to the load device.

Advantageous Effects of Invention

According to the invention described above, since the unnecessary drive of the DC-DC converter is inhibited, it is possible to reduce the power consumption of the fuel cell system.

BRIEF DESCRIPTION OF DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a system configuration view of an FCHV system according to an embodiment;

<figref idref="DRAWINGS">FIG. 2</figref> is a diagram of functional blocks for executing power control of a fuel cell system according to the present embodiment;

<figref idref="DRAWINGS">FIG. 3</figref> is a characteristic view showing a current-voltage (I-V) characteristic f<b>0</b> and a power curve indicating a fuel cell requested power P_REQof a fuel cell;

<figref idref="DRAWINGS">FIG. 4</figref> is a characteristic view showing a generated power (Pfc)-output terminal voltage (Vfc) characteristic f<b>1</b> in the fuel cell and a drive power (PM)-input terminal voltage (Vinv) characteristic f<b>2</b> in a motor;

<figref idref="DRAWINGS">FIG. 5</figref> is an example of change over time of each of a fuel cell required output voltage Vfc_REQand an inverter required input voltage Vinv_REQ;

<figref idref="DRAWINGS">FIG. 6</figref> is an example of change over time of an inverter input unit voltage Vinv when the present invention is applied in the characteristics of <figref idref="DRAWINGS">FIG. 4</figref>;

<figref idref="DRAWINGS">FIG. 7</figref> is a power control flowchart of the fuel cell system according to a present first embodiment;

<figref idref="DRAWINGS">FIG. 8</figref> is an example of a drive control command C_Vfcof a first converter <b>11</b> in the present first embodiment;

<figref idref="DRAWINGS">FIG. 9</figref> is a waveform chart for explaining timing for switching the first converter <b>11</b> according to a present second embodiment; and

<figref idref="DRAWINGS">FIG. 10</figref> is a power control flowchart of a fuel cell system according to the present second embodiment.

DESCRIPTION OF EMBODIMENTS

Next, a description will be given of preferred embodiments for carrying out the present invention with reference to the drawings.

In the following description of the drawings, the same or similar portions are designated by the same or similar reference numerals. Note that the drawings are schematic. Consequently, specific characteristics and the like should be determined by checking the following description. In addition, it will be easily understood that, among the individual drawings, portions having mutually different characteristics are included. Further, although each of the following embodiments describes that one control device executes all processing, the embodiment includes the case where a plurality of control units cooperate to complete the control processing according to the present invention.

(First Embodiment)

The present first embodiment relates to an aspect of the invention as a basic aspect of the present invention in which, the higher voltage of a required output voltage of a fuel cell and a required input voltage of an inverter is outputted as an input voltage of the inverter. In particular, the present first embodiment relates to a power control method in which the required output voltage of the fuel cell and the required input voltage of the inverter are compared with each other and, when it is judged that the required output voltage of the fuel cell is not less than the required input voltage of the inverter, the operation of a first converter is suspended.

(System Configuration)

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a fuel cell system <b>100</b> mounted on a vehicle according to the present first embodiment. Such vehicle is an FCHV (Fuel Cell Hybrid Vehicle).

The fuel cell system <b>100</b> includes a fuel cell <b>10</b>, a first converter <b>11</b>, a second converter <b>12</b>, a battery <b>13</b>, an inverter <b>14</b>, a motor <b>15</b>, an auxiliary equipment inverter <b>18</b>, a high-voltage auxiliary equipment <b>19</b>, and a control device <b>20</b>.

The fuel cell <b>10</b> is power generation means formed by stacking a plurality of unit cells in series. The unit cell has a structure in which an MEA (Membrane Electrode Assembly) obtained by sandwiching an ion exchange membrane such as a polymer electrolyte or the like between an anode electrode and a cathode electrode is sandwiched between separators. In the anode electrode, an anode-electrode catalyst layer is provided on a porous support layer, while in the cathode electrode, a cathode-electrode catalyst layer is provided on a porous support layer. To the anode electrode of each unit cell, a fuel gas (e.g., a hydrogen gas) is supplied via the separator from a fuel gas supply system which is not shown. To the cathode electrode of each unit cell, an oxidized gas (e.g., air) is supplied via the separator from an oxidized gas supply system which is not shown. The separator is formed with a passage for a coolant, and the coolant is supplied to the passage from a coolant supply system which is not shown. In the fuel cell <b>10</b>, an oxidation reaction of Expression (1) occurs in the anode electrode, a reduction reaction of Expression (2) occurs in the cathode electrode, and an electromotive reaction of Expression (3) occurs in the entire fuel cell <b>10</b>. <br />H₂→2H⁺+2<i>e</i>⁻  (1)<br />(½)O₂+2H⁺+2<i>e</i>⁻→H₂O  (2)<br />H₂+(½)O₂→H₂O  (3)<br /> By connecting a plurality of unit cells in series, the fuel cell <b>10</b> outputs an output terminal voltage Vfc to an output terminal. The fuel cell <b>10</b> has a predetermined current-voltage output characteristic, and an output current and an output power are changed correspondingly to change in the output terminal voltage Vfc.

The first converter <b>11</b> is a voltage converter, and has a configuration as a DC-DC converter. When a three-phase operation system is employed, the first converter <b>11</b> has a circuit configuration of, e.g., a three-phase bridge converter or the like. The three-phase bridge converter has switching elements including a reactor, a rectification diode, and an IGBT (Insulated Gate Bipolar ransistor). By combining these elements, there are formed a circuit part similar to an inverter in which an inputted DC voltage is temporarily converted to alternating current, and a part in which the alternating current is rectified again to be converted to a different DC voltage. Note that the circuit configuration of the first converter <b>11</b> is not limited to the above-described configuration, and any configuration capable of controlling the output terminal voltage Vfc of the fuel cell <b>10</b> can be adopted.

The first converter <b>11</b> has the output terminal of the fuel cell <b>10</b> connected on the primary side, and the input terminal of the inverter <b>14</b> connected on the secondary side. The first converter <b>11</b> is configured to control the terminal voltage on the primary side (the output terminal voltage Vfc of the fuel cell <b>10</b>) according to a command C_Vfcfor driving from the control device <b>20</b>. That is, by the first converter <b>11</b>, the output terminal voltage Vfc of the fuel cell <b>10</b> is controlled to become a voltage in correspondence to a target output (i.e., the target output terminal voltage Vfc). In addition, the first converter <b>11</b> is configured to convert the voltage such that the output terminal voltage Vfc of the fuel cell <b>10</b> and an input terminal voltage Vinv of the inverter <b>14</b> match each other. Further, when receiving a command C_Vfcfor suspending the operation from the control device <b>20</b>, the first converter <b>11</b> is configured to bring a part of the internal switching elements into an ON state so that the primary side and the secondary side are electrically directly connected.

The battery <b>13</b> is a power storage device, and functions as a storage source for surplus power of power generated in the fuel cell <b>10</b>, a storage source for regenerative energy in regenerative braking, and an energy buffer at the time of load change involved in acceleration or deceleration of a fuel cell vehicle. As the battery <b>13</b>, for example, there are used secondary batteries such as a nickel-cadmium battery, a nickel-hydrogen battery, or a lithium secondary battery. An output terminal voltage V_BATof the battery <b>13</b> serves as the input terminal voltage of the second converter <b>12</b>.

The second converter <b>12</b> is a voltage converter, and has the configuration as the DC-DC converter similar to that of the first converter <b>11</b>. The second converter <b>12</b> has the output terminal of the battery <b>13</b> connected on the primary side, and has the input terminal of the inverter <b>14</b> connected on the secondary side. The second converter <b>12</b> is configured to control the terminal voltage on the secondary side (the input terminal voltage Vinv of the inverter <b>14</b>) according to a command from the control device <b>20</b>. For example, when the requested power of the motor <b>15</b> is changed, the second converter <b>12</b> changes the input terminal voltage Vinv of the inverter <b>14</b> until the input terminal voltage Vinv reaches the set target input voltage. The second converter <b>12</b> is configured such that stepwise control is performed in which, after the input terminal voltage Vinv of the inverter <b>14</b> reaches the target input voltage, the first converter <b>11</b> controls the output terminal voltage Vfc of the fuel cell <b>10</b>. Note that, as the circuit configuration of the second converter <b>12</b>, any configuration capable of controlling the input terminal voltage Vinv of the inverter <b>14</b> can be adopted.

The inverter <b>14</b> is a power converter, and is configured to convert direct current supplied to the input terminal to alternating current and supply the alternating current to the motor <b>15</b>. The circuit configuration of the inverter <b>14</b> has, e.g., a PWM inverter circuit driven by a pulse width modulation method. The inverter <b>14</b> is configured to supply three-phase AC power having a predetermined drive voltage Vd (r.m.s. value) to the motor <b>15</b> according to a command C_vdfor specifying an inverter requested voltage from the control device <b>20</b>. In addition, the inverter <b>14</b> is configured to output the currently outputted drive voltage (the inverter output voltage) Vd to the control device <b>20</b> as a drive voltage signal S_Vd.

The motor <b>15</b> is a traction motor for running of a vehicle, and is configured to give thrust to the present vehicle when drive power is supplied thereto, and generate regenerative power when the vehicle is decelerated. A differential <b>16</b> is a deceleration device, and is configured to reduce high-speed revolution of the motor <b>15</b> at a predetermined ratio, and cause a shaft provided with tires <b>17</b> to rotate. An RPM sensor <b>23</b> is configured to detect the RPM of the motor <b>15</b> to output an RPM signal S_Nto the control device <b>20</b>.

The auxiliary equipment inverter <b>18</b> is a power converter, and is configured to convert direct current supplied to the input terminal to alternating current and supply the alternating current to the high-voltage auxiliary equipment <b>19</b>. The circuit configuration of the auxiliary equipment inverter <b>18</b> is the same as that of the inverter <b>14</b> described above. The auxiliary equipment inverter <b>18</b> is configured to supply three-phase AC power having a predetermined drive voltage Vd<b>2</b> (r.m.s. value) to the high-voltage auxiliary equipment <b>19</b> according to a command C_Vd2from the control device <b>20</b>. Note that the high-voltage auxiliary equipment <b>19</b> is a generic name for a humidifier, an air compressor, a hydrogen pump, and a coolant pump for causing the present fuel cell system <b>100</b> to function which are not shown.

The control device <b>20</b> is a computer system for controlling the fuel cell system <b>100</b>, and has, e.g. a CPU, a RAM, and a ROM. The control device <b>20</b> inputs an accelerator opening signal S_ACCin correspondence to an accelerator opening Acc from an accelerator opening sensor <b>21</b>. In addition, the control device <b>20</b> inputs various signals from a sensor group <b>22</b>, and performs various calculations required for the control. The sensor group <b>22</b> includes a current sensor for detecting the output current of the fuel cell <b>10</b>, a voltage sensor for detecting the output terminal voltage Vfc, a temperature sensor for detecting the coolant temperature of the fuel cell <b>10</b>, and an RPM sensor for detecting the RPM of the air compressor, the hydrogen pump, or the coolant pump. In addition, the control device <b>20</b> inputs the RPM signal S_Nfrom the RPM sensor <b>2113</b> for detecting the RPM N of the motor <b>15</b>.

The control device <b>20</b> refers to these signals to control the entire system.

A description will be given of the outline of the control device <b>20</b>. The control device <b>20</b> calculates a motor requested torque T_REQon the basis of the accelerator opening Acc and the motor RPM N. Then, the control device <b>20</b> calculates a motor requested power P_Mon the basis of the motor requested torque T_REQand the motor RPM N. Subsequently, the control device <b>20</b> calculates a power generation requested power P_REQon the basis of the motor requested power P_Mand the like. Then, the control device <b>20</b> calculates a requested output voltage Vfc_REQas the output terminal voltage Vfc of the fuel cell <b>10</b> required to output the power generation requested power P_FCfrom a current-voltage (I-V) characteristic of the fuel cell <b>10</b>. On an as needed basis, the control device <b>20</b> determines the allocation of the output power for the fuel cell <b>10</b> and for the battery <b>13</b>. Subsequently, the control device <b>20</b> outputs the command C_Vfcfor controlling the output terminal voltage Vfc of the fuel cell <b>10</b> such that the determined requested output voltage Vfc_REQis obtained. In addition, the control device <b>20</b> outputs the command C_Vinvto the second converter <b>12</b> to control the input terminal voltage Vinv of the inverter <b>14</b> such that the determined requested voltage of the battery <b>13</b> is extracted. Further, the control device <b>20</b> outputs the command C_vdto the inverter <b>14</b> to cause the inverter <b>14</b> to output the desired drive voltage Vd to control the torque of the motor <b>15</b> such that the motor requested torque T_REQis obtained.

In particular, the present first embodiment is characterized in that the control device <b>20</b> outputs the command C_Vdby which the higher voltage of the required output voltage Vfc_REQof the fuel cell <b>10</b> and a required input voltage Vinv_REQof the inverter <b>14</b> is outputted as the input terminal voltage Vinv of the inverter <b>14</b>.

(Functional Block)

<figref idref="DRAWINGS">FIG. 2</figref> shows a diagram of functional blocks for implementing power control of the fuel cell system <b>100</b> which are functionally implemented by the control device <b>20</b> of the present first embodiment. The control device <b>20</b> periodically or non-periodically calls a program for executing control processing according to the present invention (see <figref idref="DRAWINGS">FIG. 8</figref>), and these functional blocks are thereby functionally implemented.

Note that the functional blocks shown in <figref idref="DRAWINGS">FIG. 2</figref> have the configuration in which functions are classified for the sake of convenience, and the functions are not necessarily required to be separated as shown in <figref idref="DRAWINGS">FIG. 2</figref>. As long as the configuration is capable of controlling the input terminal voltage Vinv of the inerter <b>14</b> on the basis of inputs listed in <figref idref="DRAWINGS">FIG. 2</figref>, the same functions may be implemented by using functional blocks different from those in <figref idref="DRAWINGS">FIG. 2</figref>.

As shown in <figref idref="DRAWINGS">FIG. 2</figref>, the control device <b>20</b> includes, as the functional blocks, motor requested torque calculation means <b>201</b>, motor requested power calculation means <b>202</b>, power generation requested power calculation means <b>203</b>, fuel cell required output voltage calculation means <b>204</b>, inverter required input voltage calculation means <b>205</b>, comparison means <b>206</b>, and converter operation control means <b>207</b>.

The motor requested torque calculation means <b>201</b> calculates the output requested torque on the basis of the accelerator opening Acc acquired from the accelerator opening signal S_ACCand the RPM N of the motor <b>15</b> acquired from the RPM signal S_Nto determine the requested torque T_REQof the motor <b>15</b>. As a typical characteristic of the motor, when the RPM N of the motor and the accelerator opening Acc are determined, a generable torque is determined correspondingly to the RPM (hereinafter the characteristic is referred to as an “N-T characteristic”). The motor requested torque calculation means <b>201</b> refers to such N-T characteristic on the basis of the accelerator opening Acc, and calculates the motor requested torque T_REQ.

The motor requested power calculation means <b>202</b> is a functional block which calculates the motor requested power on the basis of the motor requested torque T_REQ. The motor requested power P_Mcorresponds to a value obtained by multiplying the motor requested torque T_REQby the RPM N (P_M=N×T_REQ).

The power generation requested power calculation means <b>203</b> is a functional block which calculates the power generation requested power P_REQof the fuel cell on the basis of the motor requested power P_M. The power generation requested power P_REQis calculated by adding the requested power of a load device other than the motor to the calculated motor requested power P_M. For example, a value obtained by adding high-voltage auxiliary equipment power P_AUXrequired in the high-voltage auxiliary equipment <b>19</b> to the motor requested power P_Mis calculated as the power generation requested power P_REQ.

The fuel cell required output voltage calculation means <b>204</b> calculates the required output voltage Vfc_REQof the fuel cell <b>10</b> on the basis of the determined power generation requested power P_REQ.

<figref idref="DRAWINGS">FIG. 3</figref> shows an output current-output voltage (I-V) characteristic f<b>0</b> and a power curve indicating the fuel cell requested power P_REQof the fuel cell <b>10</b>. During the normal operation, the fuel cell <b>10</b> changes the output current and the output voltage according to the fuel cell I-V characteristic as shown in <figref idref="DRAWINGS">FIG. 3</figref>. The fuel cell requested power P_REQdetermined by the above calculation exhibits a hyperbolic isoelectric power line indicated by a broken line in <figref idref="DRAWINGS">FIG. 3</figref>. An intersection point of the fuel cell I-V characteristic f<b>0</b> and the fuel cell requested power P_REQserves as an operation point p<b>0</b> of the present fuel cell system <b>100</b>.

The fuel cell required output voltage calculation means <b>204</b> pre-stores the fuel cell I-V characteristic f<b>0</b> of <figref idref="DRAWINGS">FIG. 3</figref> and, when the power generation requested power P_REQis determined, refers to the stored fuel cell I-V characteristic f<b>0</b> to calculate the intersection point with the determined fuel cell requested power P_REQ. This intersection point is the operation point p<b>0</b> which determines the requested output voltage Vfc_REQand a requested output current Ifc_REQof the fuel cell <b>10</b>. Note that it is also possible to refer to a fuel cell P-V characteristic f<b>1</b> described later in <figref idref="DRAWINGS">FIG. 4</figref> to determine the requested output voltage Vfc_REQof the fuel cell <b>10</b> as the fuel cell output voltage in correspondence to the fuel cell requested power P_REQ.

The inverter required input voltage calculation means <b>205</b> is a functional block which calculates the required input voltage Vinv_REQfor the inverter <b>14</b>. The required input voltage Vinv_REQof the inverter <b>14</b> is determined as the input terminal voltage Vinv of the inverter <b>14</b> required to cause the inverter <b>14</b> to output the determined motor requested power P_M.

<figref idref="DRAWINGS">FIG. 4</figref> shows a generated power (Pfc)-output terminal voltage (Vfc) characteristic (fuel cell P-V characteristic) f<b>1</b> in the fuel cell <b>10</b>, and a drive power (P_M) of the motor <b>15</b>-input terminal voltage (Vinv) of the inverter <b>14</b> characteristic (motor output characteristic) f<b>2</b>. As shown in the fuel cell P-V characteristic f<b>1</b> in <figref idref="DRAWINGS">FIG. 4</figref>, in the fuel cell <b>10</b>, as the output terminal voltage Vfc decreases, the generated power increases. In addition, as shown in the motor output characteristic f<b>2</b> in <figref idref="DRAWINGS">FIG. 4</figref>, as the drive power of the motor <b>15</b> increases, the input terminal voltage Vinv to the inverter <b>14</b> increases. In the motor output characteristic f<b>2</b> of <figref idref="DRAWINGS">FIG. 4</figref>, the drive power of the motor <b>15</b> corresponds to the motor requested power P_Mdetermined by the above calculation. The input terminal voltage Vinv of the inverter <b>14</b> corresponds to the requested input voltage Vinv_REQof the inverter <b>14</b> determined by the above calculation.

The inverter required input voltage calculation means <b>205</b> pre-stores the drive power (P_M) of the motor <b>15</b>-input terminal voltage (Vinv) of the inverter <b>14</b> characteristic as shown in the motor output characteristic f<b>2</b> of <figref idref="DRAWINGS">FIG. 4</figref>. On the basis of the determined motor requested power P_M, the inverter required input voltage calculation means <b>205</b> refers to the stored motor output characteristic f<b>2</b> to calculate the requested input voltage Vinv_REQof the inverter <b>14</b>.

The comparison means <b>206</b> is a functional block which compares the determined required output voltage Vfc_REQof the fuel cell <b>10</b> and the determined requested input voltage Vinv_REQof the inverter <b>14</b>.

In order to drive the motor <b>15</b> with the power as requested (the motor requested power P_M), the input terminal voltage Vinv determined by the motor output characteristic f<b>2</b> of <figref idref="DRAWINGS">FIG. 4</figref> needs to be inputted to the inverter <b>14</b> as the minimum voltage. Herein, in <figref idref="DRAWINGS">FIG. 4</figref>, the fuel cell P-V characteristic f<b>1</b> and the motor output characteristic f<b>2</b> intersect at an intersection point p<b>1</b> in correspondence to a power threshold value Pth. In a region B having the power higher than the power threshold value Pth, when the fuel cell <b>10</b> supplies power required for the motor <b>15</b>, the output terminal voltage Vfc of the fuel cell <b>10</b> is lower than the input terminal voltage Vinv of the inverter <b>14</b>. As a result, up to the level of the required input terminal voltage Vinv of the inverter <b>14</b>, the output terminal voltage Vfc of the fuel cell <b>10</b> should be increased. A device for performing this increase processing is the first converter <b>11</b>.

On the other hand, in a region A having the power not more than the power threshold value Pth shown in <figref idref="DRAWINGS">FIG. 4</figref>, the output terminal voltage Vfc of the fuel cell <b>10</b> is higher than the input terminal voltage Vinv of the inverter <b>14</b> required to drive the motor <b>15</b>. Therefore, in the operation in the region A, there is no necessity for further increasing the output terminal voltage Vfc of the fuel cell <b>10</b>. This is the case where the output terminal voltage Vfc of the fuel cell <b>10</b> may be supplied as the input terminal voltage Vinv of the inverter <b>14</b>.

The comparison means <b>206</b> compares the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b>. This comparison is equal to the detection of the operation on the side of the region A or on the side of the region B in the comparison with the power threshold value Pth of <figref idref="DRAWINGS">FIG. 4</figref>. The judgment is performed by the converter operation control means <b>207</b>.

The converter operation control means <b>207</b> is a functional block which causes the operation of the first converter <b>11</b> to be suspended when it is judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the required input voltage Vinv_REQof the inverter <b>14</b>. Specifically, in accordance with the above judgment, the converter operation control means <b>207</b> outputs the command C_Vfcfor suspending or continuing the operation to the first converter <b>11</b>. When receiving the command C_Vfcfor suspending the operation, the first converter <b>11</b> suspends the voltage conversion operation and maintains the primary side and the secondary side of the first converter <b>11</b> in an electrically directly connected state, i.e., a conduction state. With this, the output terminal voltage Vfc of the fuel cell <b>10</b> becomes equal to the input terminal voltage Vinv of the inverter <b>14</b>. By the above processing, to the inverter <b>14</b>, the higher voltage of the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b> is outputted.

<figref idref="DRAWINGS">FIG. 5</figref> shows an example of change over time of each of the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b>. In the fuel cell vehicle, load conditions momentarily change with change of the accelerator opening or the like. When the load conditions change, the motor requested power P_Mfluctuates. Every time the motor requested power P_Mfluctuates, as described in <figref idref="DRAWINGS">FIG. 4</figref>, the operation point moves back and forth between the region A and the region B. During the movement of the operation point in the region A, the required output voltage Vfc_REQof the fuel cell <b>10</b> is higher than the required input voltage Vinv_REQof the inverter <b>14</b>. On the other hand, during the movement of the operation point in the region B, the required input voltage Vinv_REQof the inerter <b>14</b> is higher than the required output voltage Vfc_REQof the fuel cell <b>10</b>. In <figref idref="DRAWINGS">FIG. 5</figref>, such change of each of the required output voltage Vfc_REQand the required input voltage Vinv_REQof the inverter <b>14</b> is plotted using a time axis.

<figref idref="DRAWINGS">FIG. 6</figref> shows change of the input terminal voltage Vinv supplied to the inverter <b>14</b> when the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b> change as in the example of <figref idref="DRAWINGS">FIG. 5</figref> in the fuel cell system <b>100</b> according to the present first embodiment. In the present fuel cell system <b>100</b>, by the actions of the above comparison means <b>206</b> and converter operation control means <b>207</b>, the higher voltage of the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b> is outputted as the input terminal voltage Vinv of the inverter <b>14</b>.

Therefore, as shown in <figref idref="DRAWINGS">FIG. 6</figref>, when the required input voltage Vinv_REQof the inverter <b>14</b> is higher than the required output voltage Vfc_REQof the fuel cell <b>10</b>, it is judged that the operation point is in the region B of <figref idref="DRAWINGS">FIG. 4</figref>. Consequently, the required input voltage Vinv_REQoutputted by the second converter <b>12</b> is inputted to the inverter <b>14</b>. On the other hand, when the required output voltage Vfc_REQof the fuel cell <b>10</b> is higher than the required input voltage Vinv_REQof the inverter <b>14</b>, it is judged that the operation point is in the region A of <figref idref="DRAWINGS">FIG. 4</figref>. Consequently, the operation of the first converter <b>11</b> is suspended and the directly connected state is established so that the output terminal voltage Vfc of the fuel cell <b>10</b> (i.e., the fuel cell required output voltage Vfc_REQ) is directly supplied to the inverter <b>14</b> via the first converter <b>11</b>.

Note that, when the operation point is in the region A, although the second converter <b>12</b> may increase the output terminal voltage V_SATof the battery <b>13</b> up to the level of the fuel cell required output voltage Vfc_REQ, the second converter <b>12</b> may also be brought into a disconnected state. When the second converter <b>12</b> is brought into the disconnected state, by the control in which all of the switching elements are turned off in the second converter <b>12</b> or the like, the primary side and the secondary side of the second converter <b>12</b> are electrically isolated. By establishing the disconnected state, it is possible to suppress power consumption resulting from the operation of the second converter <b>12</b>.

(Operation)

Next, with reference to the flowchart of <figref idref="DRAWINGS">FIG. 6</figref>, a description will be given of the power control processing of the fuel cell system <b>100</b> of the present first embodiment implemented by the functional blocks described above. The following control processing is periodically or non-periodically executed repeatedly. For example, in the present embodiment, it is assumed that, at every predetermined control period, a software program for executing the control processing as shown in <figref idref="DRAWINGS">FIG. 6</figref> is called.

In Step S<b>10</b>, the control device <b>20</b> judges whether or not it is control timing coming at every control period. As the result of the judgment, when it is the control timing (YES), the power control processing moves to Step S<b>11</b> where the motor requested torque calculation means <b>201</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> reads the accelerator opening signal S_ACCfrom the accelerator opening sensor <b>21</b> and reads the RPM signal S_Nfrom the RPM sensor <b>23</b>. Subsequently, the motor requested torque calculation means <b>201</b> calculates the output requested torque on the basis of the accelerator opening Acc indicated by the accelerator opening signal _SACCand the motor RPM N indicated by the RPM signal S_N, and further calculates the motor requested torque T_REQ. That is, the motor requested torque calculation means <b>201</b> refers to a data table or a relational expression showing a predetermined N-T characteristic to determine an RPM N-motor requested torque characteristic T_REQin correspondence to the accelerator opening Acc, and calculates the motor requested torque T_REQin correspondence to the motor RPM N from the N-T characteristic.

Subsequently, the power control processing moves to Step S<b>12</b> where the motor requested power calculation means <b>202</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> calculates the motor requested power P_Mon the basis of the motor requested torque T_REQ. Specifically, the value obtained by multiplying the motor requested torque T_REQby the RPM N is calculated as the motor requested power P_M(=N×T_REQ).

Next, the power control processing moves to Step S<b>13</b> where the power generation requested power calculation means <b>203</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> calculates the value obtained by adding the calculated motor requested power P_Mto the high-voltage auxiliary equipment power P_AUXrequired in the high-voltage auxiliary equipment <b>19</b> as the power generation requested power P_REQ.

Then, the power control processing moves to Step S<b>14</b> where the fuel cell required output voltage calculation means <b>204</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> refers to the fuel cell I-V characteristic f<b>0</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. Subsequently, the fuel cell required output voltage calculation means <b>204</b> determines the intersection point of the determined fuel cell requested power P_REQand the fuel cell I-V characteristic f<b>0</b> to calculate the requested output voltage Vfc_REQof the fuel cell <b>10</b>.

Next, the power control processing moves to Step S<b>15</b> where the inverter required input voltage calculation means <b>205</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> refers to the motor output characteristic f<b>2</b> as shown in <figref idref="DRAWINGS">FIG. 4</figref> to calculate the requested input voltage Vinv_REQof the inverter <b>14</b> on the basis of the determined motor requested power P_M.

Subsequently, in Step S<b>16</b>, the comparison means <b>206</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> compares the determined required output voltage Vfc_REQof the fuel cell <b>10</b> and the determined required input voltage Vinv_REQof the inverter <b>14</b>. As the result, when it is judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the required input voltage Vinv_REQof the inverter <b>14</b> (YES), the power control processing moves to Step S<b>17</b>. Then, the converter operation control means <b>207</b> shown in FIG. <b>2</b> outputs the command C_Vfcfor suspending the operation of the first converter <b>11</b> to the first converter <b>11</b>. The first converter <b>11</b> having received the command C_Vfcfor suspending the operation suspends the voltage conversion operation and electrically directly connects the primary side and the secondary side. By this operation, the output terminal voltage Vfc of the fuel cell <b>10</b> is supplied as the input terminal voltage Vinv of the inverter <b>14</b>.

On the other hand, in Step S<b>16</b>, when it is judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is lower than the required input voltage Vinv_REQof the inverter <b>14</b> (NO), the power control processing moves to Step S<b>18</b>. The converter operation control means <b>207</b> outputs the command C_Vfcfor continuing the operation of the first converter <b>11</b> to the first converter <b>11</b>. Upon reception of the command, the first converter <b>11</b> continues the operation for increasing the output terminal voltage Vfc of the fuel cell <b>10</b> up to the level of the input terminal voltage Vinv supplied to the inverter <b>14</b> by the second converter <b>12</b>.

Note that, when it is judged that it is not the control timing in Step S<b>10</b> (NO), the control processing is ended without being executed.

<figref idref="DRAWINGS">FIG. 8</figref> shows an example of the drive control command C_Vfcto the first converter <b>11</b> which is changed by the power processing described above. As shown in <figref idref="DRAWINGS">FIG. 8</figref>, when the required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the required input voltage Vinv_REQof the inverter <b>14</b>, the instruction for the drive is outputted to the first converter <b>11</b>. On the other hand, when it is judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is lower than the required input voltage Vinv_REQof the inverter <b>14</b>, the instruction for suspending the drive is outputted to the first converter <b>11</b>.

By the processing described above, during the continuation of the power processing, to the inverter <b>14</b>, the higher voltage of the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b> is outputted.

(Advantages in Present First Embodiment)

According to the present first embodiment, the following advantages are obtained.

(1) Since the higher voltage of the required output voltage Vfc_REQof the fuel cell <b>10</b> and the required input voltage Vinv_REQof the inverter <b>14</b> is selected, the output terminal voltage Vfc of the fuel cell <b>10</b> is prevented from being higher than the input terminal voltage Vinv of the inverter <b>14</b>. Therefore, the unnecessary operation of the first converter <b>11</b> is avoided and it becomes possible to suppress power consumption related to the converter operation.

(2) When it is judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the required input voltage Vinv_REQof the inverter <b>14</b>, the operation of the first converter <b>11</b> is suspended, and hence it is possible to prevent the unnecessary power conversion operation.

(3) When the instruction for the operation suspension is issued, the first converter <b>11</b> maintains the primary side and the secondary side in the electrically directly connected state, and hence it is possible to easily supply the output terminal voltage Vfc of the fuel cell <b>10</b> to the input terminal voltage Vinv of the inverter <b>14</b> by the command C_Vfcfor suspending the operation.

(4) When the second converter <b>12</b> is brought into the disconnected state while the operation of the first converter <b>11</b> is suspended, it is possible to further suppress the power consumption related to the second converter <b>12</b>.

(Second Embodiment)

The present second embodiment relates to a power control method for the fuel cell system <b>100</b> which allows stable power control without the delay of response by adding hysteresis control to the power control of the first embodiment described above.

In the present second embodiment, since the configuration of the fuel cell system <b>100</b> is the same as that in the above-described first embodiment described on the basis of <figref idref="DRAWINGS">FIGS. 1 to 6</figref>, the description thereof will be omitted by retaining the same reference numerals.

The individual configurations in the diagram of the functional blocks shown in <figref idref="DRAWINGS">FIG. 2</figref> are also the same as those in the above-described first embodiment. However, in the comparison means <b>206</b> and the converter operation control means <b>207</b>, the timing for transmitting the drive control command C_Vfcfor suspending or starting the operation to the first converter <b>11</b> is different.

<figref idref="DRAWINGS">FIG. 9</figref> shows a waveform chart for explaining timing for switching the first converter <b>11</b> according to the present second embodiment. <figref idref="DRAWINGS">FIG. 9</figref> is a view obtained by enlarging a part of the change over time of each of the fuel cell required output voltage Vfc_REQand the inverter required input voltage Vinv_REQas shown in <figref idref="DRAWINGS">FIG. 5</figref>.

In the above-described first embodiment, when it has been judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the required input voltage Vinv_REQof the inverter <b>14</b>, the operation of the first converter <b>11</b> has been suspended. In addition, when it has been judged that the required output voltage Vfc_REQof the fuel cell <b>10</b> becomes lower than the required input voltage Vinv_REQof the inverter <b>14</b>, the operation of the first converter <b>11</b> has been started.

In contrast to this, in the present second embodiment, even when the required output voltage Vfc_REQof the fuel cell <b>10</b> becomes not less than the required input voltage Vinv_REQof the inverter <b>14</b>, the operation of the first converter <b>11</b> is not suspended at this point. The operation of the first converter <b>11</b> is suspended only after the difference between the required output voltage Vfc_REQand the required input voltage Vinv_REQbecomes not less than a first margin voltage ΔV<b>1</b> serving as a margin. That is, when Expression (4) is satisfied, the operation of the first converter <b>11</b> is suspended. <br />required output voltage <i>Vfc</i>_REQ≧required input voltage <i>Vinv</i>_REQ<i>+ΔV</i>1  (4)

In addition, in the present second embodiment, the operation of the first converter <b>11</b> is started before the required output voltage Vfc_REQof the fuel cell <b>10</b> becomes lower than the required input voltage Vinv_REQof the inverter <b>14</b>. When the required output voltage Vfc_REQapproaches the required input voltage Vinv_REQ, and the difference therebetween becomes not more than a second margin voltage ΔV<b>2</b> serving as a margin, the resumption of the operation of the first converter <b>11</b> is instructed ahead of the case in the first embodiment. That is, when Expression (5) is satisfied, the operation of the first converter <b>11</b> is started. <br />required output voltage <i>Vfc</i>_REQ≧required input voltage <i>Vinv</i>_REQ<i>−ΔV</i>2  (5)

Next, with reference to the flowchart of <figref idref="DRAWINGS">FIG. 6</figref>, a description will be given of power control processing of the fuel cell system <b>100</b> of the present second embodiment.

Since Steps <b>810</b> to S<b>15</b> are the same as those in the above-described first embodiment, the description thereof will be omitted.

In Step S<b>21</b>, the comparison means <b>206</b> judges whether or not the determined required output voltage Vfc_REQof the fuel cell <b>10</b> is not less than the total voltage of the required input voltage Vinv_REQof the inverter <b>14</b> and the first margin voltage ΔV<b>1</b> by comparing them. As the result, when it is judged that the required output voltage Vfc_REQis not less than the voltage given by the required input voltage Vinv_REQ+the first margin voltage ΔV<b>1</b> (YES), the power control processing moves to Step S<b>22</b>. In Step S<b>22</b>, the converter operation control means <b>207</b> outputs the command C_Vfcfor suspending the operation of the first converter <b>11</b> to the first converter <b>11</b>. The first converter <b>11</b> having received the command C_Vfcfor suspending the operation suspends the voltage conversion operation, and electrically directly connects the primary side and the secondary side. By this operation, the output terminal voltage Vfc of the fuel cell <b>10</b> is supplied as the input terminal voltage Vinv of the inverter <b>14</b>. When it is judged that the required output voltage Vfc_REQis less than the voltage given by the required input voltage Vinv_REQ+the first margin voltage ΔV<b>1</b> (NO), the power control processing moves to Step S<b>23</b>.

Then, in Step S<b>23</b>, the comparison means <b>206</b> judges whether or not the determined required output voltage Vfc_REQof the fuel cell <b>10</b> falls within the range of the second margin voltage ΔV<b>2</b> from the required input voltage Vinv_REQof the inverter <b>14</b> by comparing them. As the result, when it is judged that the required output voltage Vfc_REQis not more than the voltage given by the required input voltage Vinv_REQ−the second margin voltage ΔV<b>2</b> (YES), the power control processing moves to Step S<b>24</b>. In Step S<b>24</b>, the converter operation control means <b>207</b> outputs the command C_Vfcfor suspending the operation of the first converter <b>11</b> to the first converter <b>11</b>. The converter operation control means <b>207</b> outputs the command C_Vfcfor continuing the operation of the first converter <b>11</b> to the first converter <b>11</b>. Upon reception of the command, the first converter <b>11</b> continues the operation for increasing the output terminal voltage Vfc of the fuel cell <b>10</b> up to the level of the input terminal voltage Vinv supplied to the inverter <b>14</b> by the second converter <b>12</b>. When it is judged that the required output voltage Vfc_REQis not within the range of not more than the voltage given by the required input voltage Vinv_REQ−the second margin voltage ΔV<b>2</b> (NO), the power control processing is ended.

By the processing described above, during the continuation of the power processing, when the required output voltage Vfc_REQof the fuel cell <b>10</b> exceeds the required input voltage Vinv_REQof the inverter <b>14</b> by the first margin voltage ΔV<b>1</b>, the inverter <b>14</b> is suspended. Therefore, as shown in <figref idref="DRAWINGS">FIG. 9</figref>, at time t<b>11</b> which is behind time t<b>10</b> when the required output voltage Vfc_REQbecomes equal to the required input voltage Vinv_REQby time Δt<b>1</b>, the operation of the first converter <b>11</b> is suspended. In addition, after the operation of the first converter <b>11</b> is temporarily suspended, when the required output voltage Vfc_REQof the fuel cell <b>10</b> falls within the range of the second margin voltage ΔV<b>2</b> from the required input voltage Vinv_REQof the inverter <b>14</b>, the operation of the inverter <b>14</b> is resumed. Therefore, as shown in <figref idref="DRAWINGS">FIG. 9</figref>, at time t<b>20</b> which is ahead of time t<b>21</b> when the required output voltage Vfc_REQbecomes equal to the required input voltage Vinv_REQagain by time Δt<b>2</b>, the operation of the first converter <b>11</b> is started.

As described above, according to the present second embodiment, after the required output voltage Vfc_REQof the fuel cell <b>10</b> becomes not less than the required input voltage Vinv_REQof the inverter <b>14</b>, the slight time Δt<b>1</b> is spent on waiting. Consequently, it is possible to suspend the first converter <b>11</b> after the input terminal voltage Vinv of the inverter <b>14</b> reliably becomes higher than the output terminal voltage Vfc of the fuel cell <b>10</b>. Therefore, it is possible to reliably suppress unnecessary power consumption.

In addition, according to the present second embodiment, the operation of the first inverter <b>11</b> is started the slight time Δt<b>2</b> before the required output voltage Vfc_REQof the fuel cell <b>10</b> becomes lower than the required input voltage Vinv_REQof the inverter <b>14</b>. Therefore, it is possible to start the power conversion of the fuel cell <b>10</b> without the delay of response to thereby prevent the shortage of power supplied to the motor <b>15</b>.

(Modification)

The present invention is not limited to the above-described embodiments, and can be appropriately modified and applied within the scope of the gist of the present invention.

For example, in each of the above-described embodiments, although the present invention has been applied to the fuel cell system <b>100</b> having the first converter <b>11</b>, the second converter <b>12</b>, and the inverter <b>14</b>, the present invention is not limited to such configuration. The present invention can also be applied to a fuel cell system having one DC-DC converter, or having three or more DC-DC converters.

Further, the present invention can also be applied to a fuel cell system in which the motor <b>15</b> can be driven by direct current and the inverter <b>14</b> is not required. In such fuel cell system, instead of the input terminal voltage Vinv of the inverter <b>14</b>, the drive voltage Vd of the motor <b>15</b> may be set as the control target voltage of the second inverter <b>12</b>.

Furthermore, the load device is not necessarily the motor. As long as the load device has the input voltage-power consumption characteristic which intersects the fuel cell P-V characteristic as shown in <figref idref="DRAWINGS">FIG. 4</figref>, the invention of the present application is applicable.

Moreover, in the above-described embodiments, although the accelerator (a gas pedal) opening Acc has been inputted as the output request, the present invention is not limited thereto. For example, in a mounting type fuel cell system, there are cases where operation means corresponding to the accelerator does not exist. Such system may be configured such that information on the output request other than the accelerator is used.

INDUSTRIAL APPLICABILITY

The fuel cell system and the control method therefor of the present invention can be mounted on and applied to not only vehicles but also other movable objects. The fuel system and the control method therefor can be applied to a train, a vessel, an aircraft, and a submarine as such movable objects. In addition, the fuel cell system and the control method therefor can be applied to not only the movable objects such as the vehicle and the like but also a stationary power source system and a mobile power source system.

REFERENCE SIGNS LIST

<ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0103"><b>10</b> . . . fuel cell, <b>11</b> . . . first converter, <b>12</b> . . . second converter, <b>13</b> . . . battery, <b>14</b> . . . inverter, <b>15</b> . . . motor, <b>16</b> . . . differential, <b>17</b> . . . tire, <b>18</b> . . . auxiliary equipment inverter, <b>19</b> . . . high-voltage auxiliary equipment, <b>20</b> . . . control device, <b>21</b> . . . accelerator opening sensor, <b>22</b> . . . sensor group, <b>23</b> . . . RPM sensor, <b>100</b> . . . fuel cell system, <b>201</b> . . . motor requested torque calculation means, <b>202</b> . . . motor requested power calculation means, <b>203</b> . . . power generation requested power calculation means, <b>204</b> . . . fuel cell required output voltage calculation means, <b>205</b> . . . inverter required input voltage calculation means, <b>206</b> . . . comparison means, <b>207</b> . . . converter operation control means, Acc . . . accelerator opening, N . . . motor RPM, P_AUX. . . high-voltage auxiliary equipment power, P_REQ. . . power generation requested power, P_M. . . motor requested power, S_ACC. . . accelerator opening signal, S_N. . . RPM signal, S_vd. . . drive voltage signal, T_REQ. . . motor requested torque, V_BAT. . . battery output terminal voltage, Vd . . . drive voltage (output voltage of inverter <b>14</b>), Vd<b>2</b> . . . drive voltage (output voltage of inverter <b>18</b>), Vfc . . . output terminal voltage of fuel cell <b>10</b>, Vinv . . . input terminal voltage of inverter <b>14</b>, Vfc_REQ. . . fuel cell required output voltage, Vinv_REQ. . . inverter required input voltage, CVfc . . . drive control command for first converter <b>11</b>, CVinv . . . drive control command for second converter <b>12</b>, ΔV<b>1</b> . . . first margin voltage, ΔV<b>2</b> . . . second margin voltage</li></ul>